First total synthesis of (+)-viroallosecurinine

The first diastereoselective chiral synthesis of (+)-viroallosecurinine, isolated from Securinega virosa as a cytotoxic alkaloid, was achieved by using a chelation-controlled addition of an alkyne moiety to the corresponding ketone, and a ring-closing metathesis, as key reactions.     

Atomic ionization potentials and electron affinities with relativistic and mass corrections

Relativistic corrections to ionization potentials (IPs) and electron affinities (EAs) of atoms with an atomic number Z≤54 are examined based on the first-order perturbation theory with an approximate Schr?dinger form of the Dirac-Coulomb-Breit Hamiltonian. Using a Hartree-Fock (HF) wave function from the numerical HF method as the unperturbed function, both the LS-non-splitting and fine-structure corrections are evaluated together with the normal and specific mass corrections. The LS-non-splitting corrections are found to be important for IPs and EAs of transition metal atoms. The fine-structure corrections are generally larger in magnitude than the LS-non-splitting corrections for the atoms of groups 13–18 with Z≥31, and can never be neglected. Comparison of the IPs and EAs presented here and experimental IPs and EAs gives an estimation of the electron correlation correction for these properties. For some light atoms, the estimated values agree with the results directly obtained from correlated calculations. Received: 28 January 1997 / Accepted: 4 March 1997     

Metal cation-induced deformation of DNA self-assembled monolayers on silicon: vibrational sum frequency generation spectroscopy

Nucleic acids possess charged phosphate groups in their backbones, which require counterions to reduce the repulsive Coulombic interactions between the strands. Herein we report how different mono- and divalent metal cations influence the molecular orientations of DNA molecules on silicon surfaces upon immobilization and hybridization. Our sum frequency generation (SFG) spectroscopy studies demonstrated that the degree of conformational variation of DNA self-assembled monolayers on silicon depends on the type of metal cations present. The molecular orientation change of immobilized single-stranded oligonucleotides correlates with DNA-cation affinity (Mg(2+) > Ca(2+) > K(+) approximately Na(+)): metal cations with the strongest affinity disrupt the structure of the underlying linker monolayer the most. Upon hybridization the trend is reversed, which is attributed to the greater ability of divalent cations to mask the negative charges on the DNA backbone. These findings provide useful information for the construction of more sensitive DNA biosensors, particularly the optimization of on-chip hybridization performance.     

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy

Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching of water in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively, in both cases. The "liquid-like" water became dominant when the PVA gel was pressed against the quartz surface. The relative intensity of the SFG signal due to the "liquid-like" water to that due to the "ice-like water" at the quartz surface modified with a self-assembled monolayer of aminopropyltrimethoxysilane (APS) became higher when the negatively charged PNaMPS gel was contacted to the APS modified quartz surface in a solution of pH = 12, where the surface was negatively charged and electrostatic repulsive interaction and low friction were present between the PNaMPS gel and the APS modified surface. It, however, did not change in a solution of pH = 2, where the surface was positively charged and electrostatic attractive interaction and very high friction were present between the PNaMPS gel and the APS modified surface. These results suggest the important role of water structure for small friction at the polymer gel/solid interface.     

Zone‐Drawn Poly(p‐phenylene) Films. Effects of Molecular Orientation on Electrical and Mechanical Properties

The electrochemically synthesized poly(p‐phenylene) film could be zone drawn by a factor of 1.57, where the orientation function (f) increased with the draw ratio (λ), regardless of the heater temperature (T_h) or applied tension (σ), and reached 0.428 for the resulting film. The electrical conductivity in the drawing direction rose with f but decreased as T_h became higher due to dedoping that occurred simultaneously with drawing. Young's modulus and tensile strength significantly increased to 4.5 GPa and 155 MPa by zone drawing from 1.1 GPa and 79 MPa of the as‐synthesized film.     

Boundary element method for spatially-periodic potential problems

In this paper, we propose a boundary element method for two-dimensional potential problems with one-dimensional spatial periodicity, which have been difficult to be solved by the ordinary boundary element method. In the presented method, we reduce the potential problems with Dirichlet and Neumann boundary conditions to integral equation problems with the periodic fundamental solution of the Laplace operator and, then, obtain approximate solutions by solving linear systems given by discretizing the integral equations. Numerical examples are also included. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role and effect of dopant ion on sorption-induced motion of polypyrrole films

The sorption-induced bending and recovery motion of PPy films containing different dopant ions have been investigated, and the interaction between water vapor and PPy was studied from sorption isotherms and kinetics. It was found that the PPy/BF₄ film exhibited the most rapid motion, and the initial speeds of bending and recovery motion were 7.9 and 5.9 mm s⁻¹, respectively. The linear expansion coefficient of the film increased in order of PPy/DBS, PPy/TsO, PPy/ClO₄, and PPy/BF₄, which is consistent with the packing density of the PPy chains (ϕ_PPy). The dual-mode sorption model applied to the isothermal sorption of water vapor to the PPy demonstrated that the Langmuir's capacity constant increased in the same order with the ϕ_PPy, while the Henry's law constant was nearly constant. The sorption kinetics obeyed Fickian despite the dimensional change of the films, and the PPy/BF₄ film had the largest diffusion coefficient of 3.13 × 10⁻⁸ cm² s⁻¹. The experimental results indicated that the kind of dopant ion was crucial to the thermodynamics and kinetics of sorption, and the quick and intensive bending motion of PPy/BF₄ films was attributed to the fast diffusion of water vapor, which caused the large dimensional change of the film.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2635–2642, 1998